Japan has officially confirmed the existence of a secret Cold War deal signed with the U.S. allowing the transit of nuclear-armed American vessels through its ports. The deal violates the three non-nuclear principles Japan set out in 1967 banning the possession, production and entry into the country of nuclear weapons.

A group of experts at the Japanese Foreign Ministry who investigated the secret pact reported to the government on Tuesday that the secret deal was signed in the 1960s, with U.S. and Japanese diplomats agreeing that the transit of nuclear arms through Japanese ports did not constitute the introduction of weapons into the country and so did not require prior consultation. The revised Japan-U.S. Security Treaty in 1960 states that the U.S. can bring nuclear weapons to the island after consultations with Tokyo.

The ultra-conservative Sankei Shimbun newspaper said in an editorial on Wednesday that the three non-nuclear principles should be revised to "2.5 principles." In other words, Japan should continue to honor the agreement. Another conservative daily, the Yomiuri Shimbun, also claimed that port stops and transits of nuclear-armed vessels should be allowed, even though the deployment of such weapons in Japan should remain prohibited. In contrast, the liberal Asahi Shimbun said Japan needs to uphold the three principles and that the country needs to "exercise leadership" to establish peace in Northeast Asia.